Certain weapons should be able to have ammunition stored in them, which can be accessed more quickly when the weapon is equipped. (Storage could be inside stocks, in shell holders, in certain special magazine wells, or attached to magazines)

There should be a key that can be tapped to examine the magazine and the ammunition within, and held to refill using loose ammunition or speed loaders, whichever can be accessed and used fastest. Hotkeying a specific speedloader or type of ammunition could be used to more easily choose the ammunition being used.

Chambered ammunition should be handled separately from ammunition in the feed device.

When swapping magazines, belts, en bloc clips, feed strips, cylinders, harmonica blocks, belt holders, or other feed devices, if a round is already chambered, it should be able to be fired before the player finishes reloading. Maybe this shouldn’t be available for all weapons, as harmonica guns and revolvers have feed systems that are made up of chambers.

By just tapping the reload button, the player should drop the old feed device before applying the new one, but by holding down the reload key the player would instead take the time to place the feed device into their inventory before applying a new one. If no feed system with ammo in it is available, pressing the reload button would instead be used to refill the current feed device.

The safety should be turned on/off by holding the key to select the firemode, rather than being another firemode to cycle through. The firemode should dictate not just how many rounds can be fired per click, but also whether the action is cycled manually or automatically and whether cartridges would be fired as soon as they enter the action or not, (which would be useful, not just for open bolt weapons, but also for fanning revolvers, slamfiring pump-actions, and marching firing bolt-actions)

When manually cycling the action, it should not act as just a slower version of semiautomatic firing, instead, only every other click would fire a shot, the others would cycle the action, which would take time and move the point of aim. How long it would take and how much, when, and in which direction point of aim moves would be impacted by the particulars of the action, and the player's skill in cycling that type of action.
Types of action the player could gain skill in manipulating could include:

Lever-actions (used in firearms like the the Henry, the Schönberger-Laumann, the volcanic pistol, and the Martini-Henry.

Single-actions (used in firearms like the Remington Rolling Block, Single action revolvers, and muskets.)

Pump-actions (used in firearms like the Remington 870, Fusil Mexico, M203, and the Burgess Folding Shotgun.)

String actions (used in bows and crossbows.)

Bolt-actions (might include firearms with drum breech actions, turn bolt actions, straight pull actions, and pistol slides, or it could be subdivided.)
Firing in Semi or Fully Automatic or using a double action revolver doesn’t train or gain the benefits of using an action.

Similarly, experience can be gained in the filling and swapping of feed devices. Methods would include:

Adding links and sections onto belts and belt holders.

Stripping cartridges off of a stripper clip.

Muzzle loading of muskets, kammerladers, cannons and Metal Storm products.
(There are other forms of speedloaders and single cartridge loading, but I'm not sure how to categorize them all.)

Feed devices should still be able to be filled through the inventory/crafting interface. Speedloaders could be used as a tool to place more cartridges at a time, place cartridges in a specific order, and/or reduce the time it takes to refill the feed device.

If a cartridge is virtually the same as another cartridge, except necked up or down to accept a different caliber bullet, they should be treated as the same cartridge, and be able to be placed in the same feed devices, but the correct caliber barrel might be necessary to get them to chamber. (Alternatively, using the wrong caliber barrel could cause catastrophic failures, inconsistent cycling, or increased parts wear.)

The weapon and viewbox should not always move as one unit. All weapons should move towards the center of the center of the viewbox, but at different speeds (with the most maneuverable weapons able to keep up as fast as the player turns, and the least maneuverable weapons being noticeably delayed in turning.) Weapon recoil could also move weapons away from the center of the viewbox. Stocks and grips would make the the point of aim and viewbox recoil together, while PGO weapons would cause recoil to point the weapon away from the center of the viewbox. Barrel weights would decrease both types of recoil, but increase scope sway and decrease maneuverability.

Using a weapon one handed (done when dual wielding, swimming, climbing, and driving) the viewbox would not recoil with the weapon, but the weapon would sway and recoil away from the center of the viewbox much more. (That way dual wielded weapons would recoil independently and the recoil from firing a handgun wouldn’t cause your car to start turning.)

Belt fed weapons should be severely penalized on movement speed, maneuverability, and deploy speed when not using a belt holder, but belt holders would only be able to hold a limited amount of links or sections.

If a cartridge is virtually the same as another cartridge, except necked up or down to accept a different caliber bullet, they should be treated as the same cartridge

Recycling and reloading spent brass please? Also, the full process of unloading and reloading ammunition would be nice. Also different types of casings. Certain calibers should have really common steel cased ammunition with brass cased ammo for that caliber less common and better manufactured.

more ideas on ammunition

After all, the effectiveness of the shot is based on the ammunition and gun. (I don’t want to have two guns firing the same ammo to do wildly different amounts of damage for the sake of “balance”. The chambered round should be the base for the damage, with the quality and length of the barrel affecting it.)

By just tapping the reload button, the player should drop the old feed device before applying the new one, but by holding down the reload key the player would instead take the time to place the feed device into their inventory before applying a new one.

I think it should be the other way around. 1 tap is to store it, 2 taps is to drop it.

Maybe weapons like machine guns would have a higher chance of ejecting purely visual cases, while weapons like bolt actions would have a higher chance of ejecting reloadable brass.

– Ejected shells could be purely visual, but using a brass catching attachment would allow the player to gain an empty shell with each shot fired.

I like the second solution better than the first. Also, lets just assume steel shells aren’t recoverable just because of their notoriety with being difficult to reload.
Also, most cheaper and more common ammo is going to have steel casings, and few are willing to reload those, so those cases will only ever be visual.
The advantage of steel cased ammo, is that steel is a little lighter than brass. Disadvantage is that you cannot reload steel casings (except irl if you’re that persistent. good luck)